Sounds pretty wild to call it unethical to buy the game because of WoC (which isn't even the one responsible for the game). I doubt their worst act even comes close to a normal Tuesday for a lot of companies you likely buy from, directly or indirectly.

You can look up Larian if you want, but they are far from a big game publisher the way EA or Rockstar is. And they are going against the trend of mtx or DRM. Pirate if you want, but using morals as an excuse for not wanting to spend money doesn't really fly in this instance.

I'm not familiar enough with licensing contracts of this nature to know whether there are royalties being paid out based on the number of copies being sold. But in the case of whether WotC is going to get paid again for another licensed Baldur's Gate game in the future, that's already a done deal. Sales from this point aren't going to matter. It's similar to how that became clear pretty quick in the case of Hogwarts Legacy.

D&D is among the most mature IPs in gaming. It's not going anywhere, and Hasbro has it right now. The most effective thing you can do is support one of its competitors, like Paizo's Pathfinder.

As for whether you should pirate it, something to weigh is that Larian is one of the good guys. This is an offline/single-player capable game, with no MTX.

I mean it's definitely licensed d&d 5e content

Ok, so looking into it, WOTC owns the D&D license, which Larian Games had to licence. So, yes it indirectly supports WOTC. They don't own a stake in the game studio, and therefore aren't directly getting revenue from this games sales. They have already received the licencing fees they would be getting for this game. It does however help WOTC since they aren't developing their own 6th edition games currently and keeps D&D relevant so in that way it does support them.

Personally I would find that a morally grey area, and will pirate the game to see if I will buy it on sale.